diff --git a/src/imp/detect/aarch64_aa64reg.rs b/src/imp/detect/aarch64_aa64reg.rs
index 8d6f765b..00e53eb7 100644
--- a/src/imp/detect/aarch64_aa64reg.rs
+++ b/src/imp/detect/aarch64_aa64reg.rs
@@ -153,18 +153,20 @@ mod imp {
             pub(crate) ctr: u64,
         }
 
-        extern "C" {
-            // Defined in sys/sysctl.h.
-            // https://man.netbsd.org/sysctl.3
-            // https://github.com/NetBSD/src/blob/432a1357026b10c184d8a0ddb683008a23cc7cd9/sys/sys/sysctl.h
-            pub(crate) fn sysctlbyname(
-                name: *const c_char,
-                old_p: *mut c_void,
-                old_len_p: *mut c_size_t,
-                new_p: *const c_void,
-                new_len: c_size_t,
-            ) -> c_int;
-        }
+        sys_fn!({
+            extern "C" {
+                // Defined in sys/sysctl.h.
+                // https://man.netbsd.org/sysctl.3
+                // https://github.com/NetBSD/src/blob/432a1357026b10c184d8a0ddb683008a23cc7cd9/sys/sys/sysctl.h
+                pub(crate) fn sysctlbyname(
+                    name: *const c_char,
+                    old_p: *mut c_void,
+                    old_len_p: *mut c_size_t,
+                    new_p: *const c_void,
+                    new_len: c_size_t,
+                ) -> c_int;
+            }
+        });
     }
 
     pub(super) unsafe fn sysctl_cpu_id(name: &[u8]) -> Option<AA64Reg> {
@@ -248,19 +250,21 @@ mod imp {
             pub(crate) const CPU_ID_AA64MMFR2: c_int = 7;
         });
 
-        extern "C" {
-            // Defined in sys/sysctl.h.
-            // https://man.openbsd.org/sysctl.2
-            // https://github.com/openbsd/src/blob/ed8f5e8d82ace15e4cefca2c82941b15cb1a7830/sys/sys/sysctl.h
-            pub(crate) fn sysctl(
-                name: *const c_int,
-                name_len: c_uint,
-                old_p: *mut c_void,
-                old_len_p: *mut c_size_t,
-                new_p: *mut c_void,
-                new_len: c_size_t,
-            ) -> c_int;
-        }
+        sys_fn!({
+            extern "C" {
+                // Defined in sys/sysctl.h.
+                // https://man.openbsd.org/sysctl.2
+                // https://github.com/openbsd/src/blob/ed8f5e8d82ace15e4cefca2c82941b15cb1a7830/sys/sys/sysctl.h
+                pub(crate) fn sysctl(
+                    name: *const c_int,
+                    name_len: c_uint,
+                    old_p: *mut c_void,
+                    old_len_p: *mut c_size_t,
+                    new_p: *mut c_void,
+                    new_len: c_size_t,
+                ) -> c_int;
+            }
+        });
     }
 
     // sysctl returns an unsupported error if operation is not supported,
@@ -512,10 +516,10 @@ mod tests {
     // `cargo check --tests --target <target>` run in CI (via TESTS=1 build.sh)
     // without actually running tests on these platforms.
     // As for constants, they are checked by static assertions generated by sys_const!.
+    // As for functions, they are checked by static assertions generated by sys_fn!.
     // See also https://github.com/taiki-e/test-helper/blob/HEAD/tools/codegen/src/ffi.rs.
     // TODO(codegen): auto-generate this test
     #[cfg(target_os = "netbsd")]
-    #[allow(clippy::no_effect_underscore_binding, clippy::used_underscore_binding)]
     const _: fn() = || {
         use imp::ffi;
         use std::mem;
@@ -551,30 +555,5 @@ mod tests {
             ac_clidr: ffi.clidr,
             ac_ctr: ffi.ctr,
         };
-        let mut _sysctlbyname: unsafe extern "C" fn(
-            *const ffi::c_char,
-            *mut ffi::c_void,
-            *mut ffi::c_size_t,
-            *const ffi::c_void,
-            ffi::c_size_t,
-        ) -> ffi::c_int = ffi::sysctlbyname;
-        _sysctlbyname = libc::sysctlbyname;
-        _sysctlbyname = sys::sysctlbyname;
-    };
-    #[cfg(target_os = "openbsd")]
-    #[allow(clippy::no_effect_underscore_binding)]
-    const _: fn() = || {
-        use imp::ffi;
-        use test_helper::sys;
-        let mut _sysctl: unsafe extern "C" fn(
-            *const ffi::c_int,
-            ffi::c_uint,
-            *mut ffi::c_void,
-            *mut ffi::c_size_t,
-            *mut ffi::c_void,
-            ffi::c_size_t,
-        ) -> ffi::c_int = ffi::sysctl;
-        _sysctl = libc::sysctl;
-        _sysctl = sys::sysctl;
     };
 }
diff --git a/src/imp/detect/aarch64_apple.rs b/src/imp/detect/aarch64_apple.rs
index 0b5a1952..7710dfa3 100644
--- a/src/imp/detect/aarch64_apple.rs
+++ b/src/imp/detect/aarch64_apple.rs
@@ -27,17 +27,19 @@ use core::{mem, ptr};
 mod ffi {
     pub(crate) use super::c_types::{c_char, c_int, c_size_t, c_void};
 
-    extern "C" {
-        // https://developer.apple.com/documentation/kernel/1387446-sysctlbyname
-        // https://github.com/apple-oss-distributions/xnu/blob/8d741a5de7ff4191bf97d57b9f54c2f6d4a15585/bsd/sys/sysctl.h
-        pub(crate) fn sysctlbyname(
-            name: *const c_char,
-            old_p: *mut c_void,
-            old_len_p: *mut c_size_t,
-            new_p: *mut c_void,
-            new_len: c_size_t,
-        ) -> c_int;
-    }
+    sys_fn!({
+        extern "C" {
+            // https://developer.apple.com/documentation/kernel/1387446-sysctlbyname
+            // https://github.com/apple-oss-distributions/xnu/blob/8d741a5de7ff4191bf97d57b9f54c2f6d4a15585/bsd/sys/sysctl.h
+            pub(crate) fn sysctlbyname(
+                name: *const c_char,
+                old_p: *mut c_void,
+                old_len_p: *mut c_size_t,
+                new_p: *mut c_void,
+                new_len: c_size_t,
+            ) -> c_int;
+        }
+    });
 }
 
 unsafe fn sysctlbyname32(name: &[u8]) -> Option<u32> {
@@ -258,28 +260,4 @@ mod tests {
             }
         }
     }
-
-    // Static assertions for FFI bindings.
-    // This checks that FFI bindings defined in this crate, FFI bindings defined
-    // in libc, and FFI bindings generated for the platform's latest header file
-    // using bindgen have compatible signatures.
-    // Since this is static assertion, we can detect problems with
-    // `cargo check --tests --target <target>` run in CI (via TESTS=1 build.sh)
-    // without actually running tests on these platforms.
-    // As for constants, they are checked by static assertions generated by sys_const!.
-    // See also https://github.com/taiki-e/test-helper/blob/HEAD/tools/codegen/src/ffi.rs.
-    // TODO(codegen): auto-generate this test
-    #[allow(clippy::no_effect_underscore_binding)]
-    const _: fn() = || {
-        use test_helper::sys;
-        let mut _sysctlbyname: unsafe extern "C" fn(
-            *const ffi::c_char,
-            *mut ffi::c_void,
-            *mut ffi::c_size_t,
-            *mut ffi::c_void,
-            ffi::c_size_t,
-        ) -> ffi::c_int = ffi::sysctlbyname;
-        _sysctlbyname = libc::sysctlbyname;
-        _sysctlbyname = sys::sysctlbyname;
-    };
 }
diff --git a/src/imp/detect/aarch64_fuchsia.rs b/src/imp/detect/aarch64_fuchsia.rs
index cdb4bac1..7a207a5a 100644
--- a/src/imp/detect/aarch64_fuchsia.rs
+++ b/src/imp/detect/aarch64_fuchsia.rs
@@ -27,6 +27,7 @@ mod ffi {
         pub(crate) const ZX_ARM64_FEATURE_ISA_ATOMICS: u32 = 1 << 8;
     });
 
+    // TODO: use sys_fn!
     #[link(name = "zircon")]
     extern "C" {
         // https://fuchsia.dev/reference/syscalls/system_get_features
@@ -80,12 +81,7 @@ mod tests {
     // As for constants, they are checked by static assertions generated by sys_const!.
     // See also https://github.com/taiki-e/test-helper/blob/HEAD/tools/codegen/src/ffi.rs.
     // TODO(codegen): auto-generate this test
-    #[allow(
-        clippy::cast_possible_wrap,
-        clippy::cast_sign_loss,
-        clippy::cast_possible_truncation,
-        clippy::no_effect_underscore_binding
-    )]
+    #[allow(clippy::cast_possible_wrap, clippy::cast_sign_loss, clippy::cast_possible_truncation)]
     const _: fn() = || {
         use test_helper::sys;
         // TODO(codegen): zx_system_get_features
diff --git a/src/imp/detect/aarch64_illumos.rs b/src/imp/detect/aarch64_illumos.rs
index 4704dfaa..a401f600 100644
--- a/src/imp/detect/aarch64_illumos.rs
+++ b/src/imp/detect/aarch64_illumos.rs
@@ -23,12 +23,14 @@ mod ffi {
         pub(crate) const AV_AARCH64_2_LSE2: u32 = 1 << 2;
     });
 
-    extern "C" {
-        // Defined in sys/auxv.h.
-        // https://illumos.org/man/2/getisax
-        // https://github.com/richlowe/illumos-gate/blob/arm64-gate/usr/src/uts/common/sys/auxv.h
-        pub(crate) fn getisax(array: *mut u32, n: c_uint) -> c_uint;
-    }
+    sys_fn!({
+        extern "C" {
+            // Defined in sys/auxv.h.
+            // https://illumos.org/man/2/getisax
+            // https://github.com/richlowe/illumos-gate/blob/arm64-gate/usr/src/uts/common/sys/auxv.h
+            pub(crate) fn getisax(array: *mut u32, n: c_uint) -> c_uint;
+        }
+    });
 }
 
 #[cold]
@@ -46,33 +48,3 @@ fn _detect(info: &mut CpuInfo) {
         info.set(CpuInfo::HAS_LSE2);
     }
 }
-
-#[allow(
-    clippy::alloc_instead_of_core,
-    clippy::std_instead_of_alloc,
-    clippy::std_instead_of_core,
-    clippy::undocumented_unsafe_blocks,
-    clippy::wildcard_imports
-)]
-#[cfg(test)]
-mod tests {
-    use super::*;
-
-    // Static assertions for FFI bindings.
-    // This checks that FFI bindings defined in this crate, FFI bindings defined
-    // in libc, and FFI bindings generated for the platform's latest header file
-    // using bindgen have compatible signatures.
-    // Since this is static assertion, we can detect problems with
-    // `cargo check --tests --target <target>` run in CI (via TESTS=1 build.sh)
-    // without actually running tests on these platforms.
-    // As for constants, they are checked by static assertions generated by sys_const!.
-    // See also https://github.com/taiki-e/test-helper/blob/HEAD/tools/codegen/src/ffi.rs.
-    // TODO(codegen): auto-generate this test
-    #[allow(clippy::no_effect_underscore_binding)]
-    const _: fn() = || {
-        use test_helper::sys;
-        let mut _getisax: unsafe extern "C" fn(*mut u32, ffi::c_uint) -> ffi::c_uint = ffi::getisax;
-        _getisax = libc::getisax;
-        _getisax = sys::getisax;
-    };
-}
diff --git a/src/imp/detect/aarch64_windows.rs b/src/imp/detect/aarch64_windows.rs
index 7eb3b875..c4f67db8 100644
--- a/src/imp/detect/aarch64_windows.rs
+++ b/src/imp/detect/aarch64_windows.rs
@@ -61,12 +61,7 @@ mod tests {
     // windows-sys' signatures/values.)
     // See also https://github.com/taiki-e/test-helper/blob/HEAD/tools/codegen/src/ffi.rs.
     // TODO(codegen): auto-generate this test
-    #[allow(
-        clippy::cast_possible_wrap,
-        clippy::cast_sign_loss,
-        clippy::cast_possible_truncation,
-        clippy::no_effect_underscore_binding
-    )]
+    #[allow(clippy::cast_possible_wrap, clippy::cast_sign_loss, clippy::cast_possible_truncation)]
     const _: fn() = || {
         let _: ffi::DWORD = 0 as windows_sys::Win32::System::Threading::PROCESSOR_FEATURE_ID;
         let _: ffi::BOOL = 0 as windows_sys::Win32::Foundation::BOOL;
diff --git a/src/imp/detect/auxv.rs b/src/imp/detect/auxv.rs
index 43d11872..680aaa05 100644
--- a/src/imp/detect/auxv.rs
+++ b/src/imp/detect/auxv.rs
@@ -137,21 +137,26 @@ mod os {
             pub(crate) const PROP_VALUE_MAX: c_int = 92;
         });
 
-        extern "C" {
-            // Defined in sys/auxv.h.
-            // https://man7.org/linux/man-pages/man3/getauxval.3.html
-            // https://github.com/bminor/glibc/blob/glibc-2.40/misc/sys/auxv.h
-            // https://github.com/bminor/musl/blob/v1.2.5/include/sys/auxv.h
-            // https://github.com/wbx-github/uclibc-ng/blob/v1.0.47/include/sys/auxv.h
-            // https://github.com/aosp-mirror/platform_bionic/blob/d3ebc2f7c49a9893b114124d4a6b315f3a328764/libc/include/sys/auxv.h
-            // https://github.com/picolibc/picolibc/blob/1.8.6/newlib/libc/include/sys/auxv.h
-            pub(crate) fn getauxval(type_: c_ulong) -> c_ulong;
-
-            // Defined in sys/system_properties.h.
-            // https://github.com/aosp-mirror/platform_bionic/blob/d3ebc2f7c49a9893b114124d4a6b315f3a328764/libc/include/sys/system_properties.h
-            #[cfg(all(target_arch = "aarch64", target_os = "android"))]
-            pub(crate) fn __system_property_get(name: *const c_char, value: *mut c_char) -> c_int;
-        }
+        sys_fn!({
+            extern "C" {
+                // Defined in sys/auxv.h.
+                // https://man7.org/linux/man-pages/man3/getauxval.3.html
+                // https://github.com/bminor/glibc/blob/glibc-2.40/misc/sys/auxv.h
+                // https://github.com/bminor/musl/blob/v1.2.5/include/sys/auxv.h
+                // https://github.com/wbx-github/uclibc-ng/blob/v1.0.47/include/sys/auxv.h
+                // https://github.com/aosp-mirror/platform_bionic/blob/d3ebc2f7c49a9893b114124d4a6b315f3a328764/libc/include/sys/auxv.h
+                // https://github.com/picolibc/picolibc/blob/1.8.6/newlib/libc/include/sys/auxv.h
+                pub(crate) fn getauxval(type_: c_ulong) -> c_ulong;
+
+                // Defined in sys/system_properties.h.
+                // https://github.com/aosp-mirror/platform_bionic/blob/d3ebc2f7c49a9893b114124d4a6b315f3a328764/libc/include/sys/system_properties.h
+                #[cfg(all(target_arch = "aarch64", target_os = "android"))]
+                pub(crate) fn __system_property_get(
+                    name: *const c_char,
+                    value: *mut c_char,
+                ) -> c_int;
+            }
+        });
     }
 
     pub(super) fn getauxval(type_: ffi::c_ulong) -> ffi::c_ulong {
@@ -202,17 +207,19 @@ mod os {
             pub(crate) const AT_HWCAP2: c_int = 26;
         });
 
-        extern "C" {
-            // FreeBSD
-            // Defined in sys/auxv.h.
-            // https://man.freebsd.org/elf_aux_info(3)
-            // https://github.com/freebsd/freebsd-src/blob/release/14.1.0/sys/sys/auxv.h
-            // OpenBSD
-            // Defined in sys/auxv.h.
-            // https://man.openbsd.org/elf_aux_info.3
-            // https://github.com/openbsd/src/blob/ed8f5e8d82ace15e4cefca2c82941b15cb1a7830/sys/sys/auxv.h
-            pub(crate) fn elf_aux_info(aux: c_int, buf: *mut c_void, buf_len: c_int) -> c_int;
-        }
+        sys_fn!({
+            extern "C" {
+                // FreeBSD
+                // Defined in sys/auxv.h.
+                // https://man.freebsd.org/elf_aux_info(3)
+                // https://github.com/freebsd/freebsd-src/blob/release/14.1.0/sys/sys/auxv.h
+                // OpenBSD
+                // Defined in sys/auxv.h.
+                // https://man.openbsd.org/elf_aux_info.3
+                // https://github.com/openbsd/src/blob/ed8f5e8d82ace15e4cefca2c82941b15cb1a7830/sys/sys/auxv.h
+                pub(crate) fn elf_aux_info(aux: c_int, buf: *mut c_void, buf_len: c_int) -> c_int;
+            }
+        });
     }
 
     pub(super) fn getauxval(aux: ffi::c_int) -> ffi::c_ulong {
@@ -370,6 +377,12 @@ mod arch {
 )]
 #[cfg(test)]
 mod tests {
+    #[cfg(not(target_os = "openbsd"))]
+    #[cfg(not(all(
+        target_os = "linux",
+        target_arch = "aarch64",
+        target_pointer_width = "32",
+    )))]
     use super::*;
 
     #[allow(clippy::cast_sign_loss)]
@@ -817,47 +830,4 @@ mod tests {
             getauxval_sysctl_no_libc(ffi::AT_HWCAP2).unwrap_or_else(hwcap2_else)
         );
     }
-
-    // Static assertions for FFI bindings.
-    // This checks that FFI bindings defined in this crate, FFI bindings defined
-    // in libc, and FFI bindings generated for the platform's latest header file
-    // using bindgen have compatible signatures.
-    // Since this is static assertion, we can detect problems with
-    // `cargo check --tests --target <target>` run in CI (via TESTS=1 build.sh)
-    // without actually running tests on these platforms.
-    // As for constants, they are checked by static assertions generated by sys_const!.
-    // See also https://github.com/taiki-e/test-helper/blob/HEAD/tools/codegen/src/ffi.rs.
-    // TODO(codegen): auto-generate this test
-    #[allow(clippy::no_effect_underscore_binding)]
-    const _: fn() = || {
-        use test_helper::sys;
-        #[cfg(any(target_os = "linux", target_os = "android"))]
-        {
-            let mut _getauxval: unsafe extern "C" fn(ffi::c_ulong) -> ffi::c_ulong = ffi::getauxval;
-            _getauxval = libc::getauxval;
-            _getauxval = sys::getauxval;
-        }
-        #[cfg(all(target_arch = "aarch64", target_os = "android"))]
-        {
-            let mut ___system_property_get: unsafe extern "C" fn(
-                *const ffi::c_char,
-                *mut ffi::c_char,
-            ) -> ffi::c_int = ffi::__system_property_get;
-            ___system_property_get = libc::__system_property_get;
-            ___system_property_get = sys::__system_property_get;
-        }
-        #[cfg(any(target_os = "freebsd", target_os = "openbsd"))]
-        {
-            let mut _elf_aux_info: unsafe extern "C" fn(
-                ffi::c_int,
-                *mut ffi::c_void,
-                ffi::c_int,
-            ) -> ffi::c_int = ffi::elf_aux_info;
-            #[cfg(not(target_os = "openbsd"))] // libc doesn't have this on OpenBSD
-            {
-                _elf_aux_info = libc::elf_aux_info;
-            }
-            _elf_aux_info = sys::elf_aux_info;
-        }
-    };
 }
diff --git a/src/imp/detect/common.rs b/src/imp/detect/common.rs
index ccb6b4fa..028471a4 100644
--- a/src/imp/detect/common.rs
+++ b/src/imp/detect/common.rs
@@ -127,6 +127,8 @@ flags! {
 #[allow(dead_code, unused_macros, non_camel_case_types)]
 #[macro_use]
 mod c_types {
+    /// Defines constants with #[cfg(test)] static assertions which checks
+    /// values are the same as the platform's latest header files' ones.
     // Note: This macro is sys_const!({ }), not sys_const! { }.
     // An extra brace is used in input to make contents rustfmt-able:.
     macro_rules! sys_const {
@@ -159,6 +161,42 @@ mod c_types {
             };
         };
     }
+    /// Defines functions with #[cfg(test)] static assertions which checks
+    /// signatures are the same as the platform's latest header files' ones.
+    // Note: This macro is sys_fn!({ }), not sys_fn! { }.
+    // An extra brace is used in input to make contents rustfmt-able:.
+    macro_rules! sys_fn {
+        ({
+            $(#[$extern_attr:meta])*
+            extern $abi:literal {$(
+                $(#[$fn_attr:meta])*
+                $vis:vis fn $name:ident($($arg_pat:ident: $arg_ty:ty),* $(,)?) $(-> $ret_ty:ty)?;
+            )*}
+        }) => {
+            $(#[$extern_attr])*
+            extern $abi {$(
+                $(#[$fn_attr])*
+                $vis fn $name($($arg_pat: $arg_ty),*) $(-> $ret_ty)?;
+            )*}
+            // Static assertions for FFI bindings.
+            // This checks that FFI bindings defined in this crate and FFI bindings generated for
+            // the platform's latest header file using bindgen have the same signatures.
+            // Since this is static assertion, we can detect problems with
+            // `cargo check --tests --target <target>` run in CI (via TESTS=1 build.sh)
+            // without actually running tests on these platforms.
+            // See also https://github.com/taiki-e/test-helper/blob/HEAD/tools/codegen/src/ffi.rs.
+            #[cfg(test)]
+            const _: fn() = || {
+                $(
+                    $(#[$fn_attr])*
+                    {
+                        let mut _f: unsafe extern $abi fn($($arg_ty),*) $(-> $ret_ty)? = $name;
+                        _f = test_helper::sys::$name;
+                    }
+                )*
+            };
+        };
+    }
 
     pub(crate) type c_void = core::ffi::c_void;
     // c_{,u}int is {i,u}32 on non-16-bit architectures
diff --git a/src/imp/detect/riscv_linux.rs b/src/imp/detect/riscv_linux.rs
index ae102d40..a223b4b7 100644
--- a/src/imp/detect/riscv_linux.rs
+++ b/src/imp/detect/riscv_linux.rs
@@ -37,6 +37,7 @@ mod ffi {
         pub(crate) const RISCV_HWPROBE_EXT_ZACAS: u64 = 1 << 34;
     });
 
+    // TODO: use sys_fn!
     #[cfg(not(all(
         target_os = "linux",
         any(target_arch = "riscv32", all(target_arch = "riscv64", target_pointer_width = "64")),
@@ -159,7 +160,6 @@ mod tests {
     // As for constants, they are checked by static assertions generated by sys_const!.
     // See also https://github.com/taiki-e/test-helper/blob/HEAD/tools/codegen/src/ffi.rs.
     // TODO(codegen): auto-generate this test
-    #[allow(clippy::no_effect_underscore_binding)]
     const _: fn() = || {
         use std::mem;
         use test_helper::sys;